The one I like best of all is Churchill by Andrew Roberts. It really gives you the flavor of the human being and his history.
There are no perfect human beings.
He was always controversial during his own lifetime, but one thing to remember is he was a product of the 19th Century, the Victorian era. Many of his views reflected that. We're all products of the eras we grow up in to some degree.
Regardless, there's no doubt that his leadership in Britain's decision to carry on against Hitler, his very personal diplomacy with the US that resulted in Lend Lease and the lifting of isolationist restrictions in the US on helping arm Britain (and later Russia after June, 1941) and sustain her during that crucial year of 1940-41, his ability to get past his anti-Communism and work with Stalin to win the war even before Pearl Harbor, were crucial to the outcome, and in my opinion without him the world would be different today -- not in a good way.
Churchill was behind the decision to save more than 300,000 men with the Dunkirk evacuation. He understood the necessity of preserving the RAF for defense and not send additional planes to France after the French were clearly beaten. He was behind the decisions made during the Battle of Britain, when all Britain had left was air and sea power.
These decisions took guts and were both necessary and intelligent.
In fact, his warnings beginning in the early '30s about the dangers of Nazism and the lack of preparation among the Western democracies were prescient, proved correct, and that's a big reason he was given the Premiership in May of 1940.
People fail to credit Churchill with having his military leadership do a study regarding whether Britain could in fact resist and invasion, and understanding that study before deciding to carry on. They fail to credit his efforts to get the US to work with them to create the Joint Chiefs of Staff and create a military alliance that actually worked, instead of each country proceeding in an uncoordinated way (the Axis countries never coordinated their military efforts, and failed miserably). They fail to credit his recognition of the necessity and value of code breakers at Bletchley Park. I could go on and on. They fail to credit his willingness to share nuclear research with the US when it became clear the Nazis were trying to develop atomic weapons.
There are so many things he did right.
Churchill and other democratic leaders of his era in the West were giants among men. Churchill, FDR, Eisenhower, Marshall, de Gaulle, and a number of others. All of them, even paranoid Stalin, respected Churchill.
Everyone has their flaws; Churchill had many. But he also had determination, grit, an ethical stance, and brilliance.
I also think the Labour government that was voted in immediately after the war got a lot less done than Churchill would have, and was part of the reason that Britain had to maintain rationing, etc.,